Conventionally, truck tractors have been coupled to a semi-trailer by a coupling device commonly referred to as a "fifth wheel". Accordingly, the truck tractor has a "fifth wheel" comprising a substantially round flat plate positioned in a substantially horizontal plane to form a tractor bearing surface. The semi-trailer includes a kingpin extending downwardly to locate and seat with the locking mechanism in the fifth wheel of the tractor. The trailer further includes a trailer bearing surface to match the tractor bearing surface. Once coupled, the tractor and trailer can pivot about the kingpin to permit the truck and trailer to articulate when turning. Because the tractor bearing plate necessarily bears a large portion of the trailer weight, much friction between the two bearing surfaces is developed. This friction adversely affects vehicle handling, increases tire wear, fatigues the driver, impairs safety and causes premature wear and damage to the truck and trailer chassis and their related components.
To reduce this friction, a lubricant such as grease has been placed between the truck tractor and semi-trailer upper coupler assembly. However, it is difficult to maintain a satisfactory layer of grease between the two bearing surfaces, thus requiring the grease to be often replenished. In addition, grease is environmentally unfriendly and very messy, attracts dirt and falls from the tractor to the road surface, thus becoming a hazard to vehicles. Further, as the grease dissipates, the handling and performance characteristics of the truck tractor and semi-trailer deteriorate such that oversteer is experienced creating an unsafe condition.
To eliminate the need for a layer of grease, ball and roller bearings have been utilized to permit the tractor bearing surface itself to rotate. However such coupling devices are relatively complex, expensive, heavy, difficult to maintain and commercially unacceptable.
Additionally, when pulling an empty trailer, especially one of today's lightweight aluminum trailers, the trailer bearing surface tends to bounce on the tractor bearing surface. This vibration is transmitted into the tractor cab, further adding to the fatigue and discomfort of the driver. Likewise, metal fatigue to the truck tractor and semi-trailer increases.
The friction also leads to wear on the kingpin. While other components of the trailer bearing are lubricated, the kingpin experiences wear from the pulling and turning by the tractor. The kingpin is often difficult to replace because it is welded in place or bolts which hold the kingpin in place are difficult or impossible to reach.
Furthermore, pulling, turning, and changing directions exert a great deal of force on the trailer bearing. Under the force of the loaded trailer and the tractor, the trailer bearing will often fail. This could lead to lost loads and accidents.
Most methods of producing the trailer bearing plate consist of a series of plates and attachments methods such as welds, bolts, or rivets. For instance, U.S. Pat. No. 2,665,177 to Schaefer is directed toward a trailer bearing. The trailer bearing comprises a lubricant retainer. The kingpin is riveted to an upper plate. U.S. Pat. No. 2,958,541 to Bar describes a replaceable kingpin mounting. The mounting comprises a pair of plates and a plurality of bolts. One plate has an opening for accepting the kingpin. The second plate has a recess for accepting the kingpin. The plates are welded together, and the bolts hold the kingpin to the second plate. U.S. Pat. No. 5,411,281 to Poirier is directed to a trailer bearing comprising a rotatable kingpin. The kingpin is mounted within a housing to allow rotation.
The present invention is provided to solve the problems stated herein as well as other problems.